Polyamides, known commercially as nylons, have excellent hardness, abrasion resistance, chemical resistance, and other mechanical properties, but suffer from being brittle. Many attempts have been made to make polyamides less brittle by blending them with impact modifiers such as rubbery polymers. For instance, U.S. Pat. No. 4,174,358 discloses the use of functionalized rubbers as impact modifiers for polyamides and U.S. Pat. Nos. 4,427,828 and 4,628,072 disclose the use of acid functionalized, hydrogenated block copolymers of styrene and dienes as similar impact modifiers. The inclusion of polar functional groups on the modifiers is generally considered to be necessary for the polyamides to be acceptably compatible with rubbers which do not otherwise contain polar functionality.
The use of acid derivative functionalized hydrogenated styrenic block copolymers as impact modifiers has been found to be particularly effective in modifying polyamides which are prepared by copolymerizing diamines and dicarboxylic acids, for example, Nylon 6,6. However, polyamides which are prepared by polymerizing monoaminocarboxylic acids or internal lactams thereof, such as Nylon 6, are more difficult to toughen with acid functionalized hydrogenated block copolymers.
U.S. Pat. No. 5,242,975 describes a process for producing impact modified blends of these functionalized block copolymers and nylons like Nylon 6 which are herein generally referred to alpha polyamides and have carboxylic acid or a derivative thereof as one terminal group and an amine as another terminal group. These alpha polyamides may be formed by ring-opening of lactams and polymerization of monoaminocarboxylic acids. The method of making a good impact modified Nylon 6 blend comprises blending a masterbatch which contains 15 to 120 parts of the alpha-polyamide and 100 parts of the functionalized block copolymer. This masterbatch is then later blended with a sufficient amount of the alpha-polyamide to result in a total of from 200 to 2000 parts by weight of the alpha-polyamide in the resultant toughened alpha-polyamide composition.
While the afore-mentioned masterbatch method works quite well, it does suffer from the following disadvantages: a specific extruder and feeder system is needed to be able to easily control the polymer feed rates and to maintain a constant blend composition. Therefore, it can be seen that it would be highly advantageous to be able to produce blends of alpha polyamides (Nylon 6) and functionalized block copolymers with excellent impact properties by direct blending. The present invention provides such compositions.